I would guess it would work with the higher classes, considering they made it support a 32gb card..

But on the whole class thing, I have never had a problem with my class 2. It does take some time to move a PSX ROM from my PC to my Phone, but imo not worth the extra money to get a better class that wont increase it that much. Remember, the class rating is only he write speed, not the read speed.

It can work for different class. The difference is the speed. The higher the class, the faster in speed in transferring data. However, whether you can maximize the speed, it depends on your device. For camera, higher class is really better, therefore you can see some CF card going to have class 10. However, for mobile, class 2 or 4 is enough.